Fouling rate reduction in heated hydrocarbon streams with degraded polyisobutylene

ABSTRACT

The deposition of fouling deposits within process equipment operated at elevated temperatures in the presence of hydrocarbons is reduced by combining with the liquid hydrocarbon a foulant inhibiting amount of mechanically degraded polyisobutylene.

United States Patent Dvoracek et a1.

[15] 3,668,l l l 51 June 6, 1972 [54] FOULING RATE REDUCTION IN HEATEDHYDROCARBON STREAMS WITH DEGRADED POLYISOBUTYLENE [72] Inventors: LouisM. Dvoracek, Brea; Amir M. Sarem,

Yorba Linda, both of Calif.

[73] Assignee: Union Oil Company of California [22] Filed: July 16, 1970{21] Appl.No.: 55,594

[52] US. Cl ..208/48 AA, 44/80, 252/59,

252/68 [51] lnt.C1 ..Cl0g 9/16,C10g 9/36,C23f14/00 [58] Field of Search..208/48; 252/59; 44/80; 203/7 [56] References Cited UNITED STATESPATENTS 3,172,892 3/1965 Le Suer et a1 ..260/376.5

Primary Examiner-Delbert E. Gantz Assistant Examiner-G. E. SchmitkonsAnomey-Milton W. Lee, Richard C. Hartman, Lannas S. Henderson, DeanSandford, Robert E. Strauss and Michael H. Laird 57 ABSTRACT Thedeposition of fouling deposits within process equipment operated atelevated temperatures in the presence of hydrocarbons is reduced bycombining with the liquid hydrocarbon a foulant inhibiting amount ofmechanically degraded polyisobutylene.

8 Claims, No Drawings FOULING RATE REDUCTION IN HEATED HYDROCARBONSTREAMS WITH DEGRADED POLYISOBUTYLENE BACKGROUND OF THE INVENTION Thenumerous processes involved in modifying the physical and chemicalproperties of hydrocarbon oils such as reforming, hydroforming,hydrocracking, isomerization, cracking fractionation, hydrofining andthe like, almost without exception, necessitate exposure of thehydrocarbon feed to relatively elevated temperatures. These temperaturesare most commonly attained by the use of heat exchangers in which thehydrocarbon feeds, products or intermediates are intimately contactedwith heat exchange surfaces. Several of the areas in which this problemwas first observed to be a limiting factor include preheat exchangers ofcrude units, hydrodesulfurizers and fluid catalytic cracking systems.Other problem areas include overhead condeners, reformer reboilers,coker furnaces, vacuum tower and alkylation reboilers, and deethanizers.Although the problems associated with fouling deposit fonnation areprobably most acute in the hydrocarbon processing industry, they are byno means limited to those systems. For example, difficulties associatedwith fouling deposition have also been recognized in petrochemicalprocessing units producing ethylene, styrene, butadiene, isoprene,acrylonitrile and other chemicals.

The problems associated with equipment fouling are well recognized inthe art as discussed in Petroleum Products", Guthrie, (McGraw Hill,l960), pp. l-l3. It is also generally recognized that these problems arenot necessarily limited to heat exchange apparatus as such. On thecontrary, the formation of fouling deposits accompanying the thermallyinitiated physical or chemical modification of the hydrocarbon stream orselected constituents thereof is observed almost any time thehydrocarbon phase is exposed to a retaining surface, metallic orotherwise, at elevated temperatures in process equipment such asfractionating columns, reactors, intermediate piping, heat exchangeequipment and the like.

Deposits of this nature are known to materially decrease heat transfercharacteristics of the affected systems and are generally removed onlywith considerable difficulty. The consequent increases in operating andmaintenance expense accompanying the formation of such deposits areoften substantial. Consequently, considerable effort has already beendevoted to the solution of these problems with the result that numerousalternative procedures have been proposed for either preventing foulantdeposition or removing fouling deposits. These alternatives have metwith varying degrees of success.

The fouling deposits which are encountered as a result of the physicaland/or chemical modification in the hydrocarbon feed initiated by theelevated process temperatures may consist of sticky, tarry, polymeric orcarbonaceous material. The most common fouling deposits can be generallyclassified as inorganic salts, corrosion products (metallic oxides andsulfides), metal-organic compounds, organic polymers and coke. Theinorganic salts such as sodium, calcium and magnesium chloride areprobably carried into the process system with the crude feedstock. Themetal organic compounds may also be present in the original feed or maybe formed on heat transfer surfaces by combination with corrosionproducts or other metals carried into the system with the processstream. The formation of organic polymers is most commonly attributed toreaction of unsaturated hydrocarbons. However, polymers can also beformed by the reaction of nitrogen and sulfur containing organiccompounds which are believed to polymerize via a mechanism involvingoxygen usually in the presence of a metal catalyst. It has beensuggested that these metal catalysts may be either corrosion products,i.e., sulfurization or oxidation products, metal-organic compounds orfree metal either carried into the system with the process stream oravailable on the interior surfaces of processing equipment. Cokedeposition is usually correlated with the occurrence of hot spots causedby the accumulation of other fouling deposits. Consequently, it can beseen that the metal and organic portions of these fouling depositsinteract and influence each other. Thus, any effort to completelycontrol or eliminate fouling deposit formation should include theelimination of both the metal contaminants related to corrosion and theorganic polymers referred to.

Fouling deposits may have organic contents as high as percent. However,such deposits typically contain much higher proportions of inorganicsubstances usually bound together with an inorganic, polymeric or tarrymatrix. For example, a typical deposit isolated during the course ofthese investigations contained 2 weight-percent silica, 38weight-percent Fqo 1 percent alumina, 18 percent sulfur determined as S0and 41 percent organic material determined by loss on ignition. Thenature of such deposits leads one to the conclusion that fouling resultsfrom a rather complex process involving the occurrence of manyreactions.

The inorganic constituents of these fouling deposits may be present dueto lack of adequate filtering of the hydrocarbon, e.g., crude or toppedcrude feed, while the scale deposits generally result fromdeterioration, i.e., corrosion, of the process equipment. The inorganicsalts are most commonly derived from crude oils which have not beensufi'rciently desalted prior to processing. However, in some instancesit has been found most expeditious to bypass desalination if the saltcontent of the crude stock, for example to a pipe still, does not exceed20 pounds per 1,000 barrels. The presence of these inorganic salt andscale components, although undesirable, does not of itself impose asubstantial burden on any given process. However, when combined with thetarry or carbonaceous organic fouling deposits these materialscontribute to the formation of tenaceous deposits which can be removedonly with considerable difficulty.

Several of the approaches taken to minimize these effects involvepolishing or coating of the interior process equipment in an effort toreduce their affinity for the organic foulants. However, it ispractically impossible to prevent the formation of these deposits bycoating the metal surfaces with protective permanent coating without aconsequent loss of process efficiency due to the inescapable loss ofheat transfer capacity attributable to the coating itself. Nevertheless,such procedures are definitely beneficial in many instances.

Yet another alternative which does not necessitate the expense involvedin process equipment coating and does not result in the accompanyingloss in heat transfer capacity involves the addition of chemicalconstituents to the hydrocarbon feed which act to either prevent theformation of foulant material or to prevent its adhesion to processequipment. Numerous compositions each of which serve to perform one ormore desirable functions have been devised for the purpose of preventingor mitigating the efiects of fouling deposit formation in processsystems. Usually these compositions are designed to operate as eithermetal deactivators, corrosion inhibitors, detergents, dispersants oranti-oxidants. In addition, it is also advantageous to formulatecompositions that perform more than one of these functions at the sametime in order to combat a plurality of undesirable effects.

Corrosion inhibitors suitable for these purposes have been discussed indetail by previous investigators such as, Bregman in his book CorrosionInhibitors, MacMillan Company, New York, Collier-MacMillan Ltd., London,1963. Exemplary of conventional corrosion inhibitors are monoandpolyamines, monoand polyamides and polyethoxlated amines having about 5to about 200 carbon atoms per molecule, and the salts of organic andinorganic acids such as acidic, oleic, dimeric, naphthenic, andphosphoric acids. This class of compounds is intended to includepolyfunctional amphoteric compounds such as aminocarboxylic acidscontaining dissimilar functional groups, e.g., amino and carboxylategroups or linkages. The most common corrosion inhibiting compositionsemployed in such applications are the relatively high molecular weightamines preferably the cyclic or endocyclic secondary amines having about18 to about 50 carbon atoms and one to about 3 amino groups per moleculesimilar to those described in connection with the detergent-dispersantcompositions, infra. The

substituted and unsubstituted imadazolines, amines and aliphatic acidsalts are illustrative of compounds within this class havingeffectiveness as corrosion inhibitors. These compositions are usuallyemployed in concentrations within a range of l to about 1,000 ppm.

Several metal deactivators have found considerable commercial successexemplary of which are N,N-disalicylidene-1, Z-diaminopropane marketedby Ethyl Corporation as Ethyl metal deactivator and N,N -disalicylidenel2- propanediamine in an organic solvent marketed as DMD by DuPont. Themetal deactivators are usually employed to complex or otherwise inhibitthe chemical activity of metals originally present in hydrocarbon streamor picked up by contact with processing equipment. As a general rulevery minor concentrations of these deactivators are effective foraccomplishing the prescribed purpose. These concentrations are usuallywithin the range of about 0.1 to about 1,000 ppm based on totalhydrocarbon.

A number of detergent compositions have found varying degrees ofcommercial acceptance. These compositions also often serve asdispersants when such functionability is desired.

Exemplary of effective detergents, which also generally exhibitdispersant properties are the sulfonates, usually including the normaland basic metal salts of petroleum sulfonic (mahogany) and long chainalkyl substituted benzene sulfonic acids usually having about eight toabout 100 carbon atoms and up to about 5 sulfonic acid or sulfonategroups per molecule; phosphonates and/or thiophosphonates, including thenormal and basic salts of the phosphonic and/or thiophosphonic acidsobtained from the reaction of polyolefms such as polyisobutenes withinorganic phosphorus agents, principally phosphorus pentasulfide;phenates including the normal and basic metal salts of alkylphenols,alkylphenol sulfides, and alkylphenol-aldehyde condensation productsusually having up to about 20 carbon atoms per molecule; alkylsubstituted salicylates including the normal andb asic metal salts,especially the carboxylate and carboxylate-phenate salts, of long chainalkyl substituted salicylic acids; alkenyl succinimides having about 20to about 200 carbon atoms per molecule, alkali metal naphthenates havingabout to about 30 carbon atoms; and primary and secondary amines andcarboxylic acids generally having about 10 to about 50 carbon atoms andup to about four amino groups. The most effective high molecular Weightamines presently employed to any substantial degree are the endocyclicfive and six membered substituted cyclic amines such as imidazoline. Oneor more of these detergent-dispersant com.- positions can be employed incombination in any given application. Although very minor concentrationsof these constituents are effective in somewhat reducing the degree offoulant deposit accumulation they are generally employed inconcentrations within a range of about 1 to about 1,000 ppm.

Currently, the most popular oxidation inhibitors are those formulatedwith the view of producing a composition having the ability to reduceorganic peroxide concentration in a hydrocarbon process stream therebyinterrupting chain oxidation reactions. Exemplary of effectiveanti-oxidants are the hydrocarbyl sulfides, disulfides, sulfoxides,phosphites, monoand poly-acyclic and cyclic amines such as thecondensation products of cyclohexylamine or aromatic diamines withcatechol, its alkaline derivatives and/or alkyl phenols, substituted andunsubstituted phenols, selenides and zinc dithiophosphates. Similarcompositions are described in more detail in U.S. Pat. No. 3,342,723.Anti-oxidant compositions also often contain compounds possessing one ormore of these functional groups such asN,N'-di-sec-butyl-p-phenylenediamine, N,N'-butyl-p-aminophenol,2,6-di-t-butyl-pcresol and the like.

As mentioned above, fouling inhibitor compositions are often formulatedwith the view of preventing or inhibiting one or more undesirablefouling reactions. Hence, these additives often contain poly-functionalcompounds or one or more compounds having dissimilar functional groups.Exemplary of commercially available poly-functional additives arePolyflo and marketed by Universal Oil Products. Polyflo 135 is believedto comprise alkyl substituted ethoxylated catechol and a corrosioninhibitor comprising a long chain dimeric aliphatic acid and a primaryamine. Polyflo 140 is believed to comprise a polyhydroxy ethoxylatedamine. These compositions are described in more detail in U.S. Pat. No.3,062,744 incorporated herein by reference. Another composition marketedas a fouling inhibitor is Betz AF-l04 marketed by Betz Laboratories ofPhiladelphia, Pa. This composition is believed to comprise a metaldeactivator similar to those above described, a bi-functional phenolicamine and an alkyl substituted succinimide. Succinimides of this natureare described in U.S. Pat. No. 3,380,909. Similar compositions arediscussed in more detail in U.S. Pat. Nos. 3,271,295, 3,271,296 and3,437,583 incorporated herein by reference.

Nalco 261, available from Nalco Chemical Company, is also a commerciallyavailable fouling inhibitor and is believed to contain morpholine and awater soluble salt of ethoxylated imidazoline. Similar compositions arediscussed more comprehensively in U.S. Pat. Nos. 3,105,810, 3,261,774and 3,224,957 incorporated herein by reference. Tretolite Aftol-2l,designed primarily for the prevention of fouling in process heatexchange equipment, is marketed by the Petrolite Corporation and isbelieved to consist primarily of Succinimides.

It should be observed that the exact composition of these fonnulationsis not generally made public by the manufacturers of the respectivecompositions and can be at best only approximated analytically byconsiderable effort. Nevertheless, the presence of certain functionalgroups can be established with relatively certainty and to a degreesufficient to illustrate the effectiveness of the compositions of thisinvention relative to previously described compositions. In addition,these compositions and information regarding their use are of courseavailable from the respective manufacturers noted above.

Unfortunately none of the expedients intended to reduce depositformation thus far developed are successful in completely eliminatingthis source of difiiculty in hydrocarbon processing. Consequently,efiorts are continuing to effect even greater improvement in both thephysical and chemical systems involved in these operations to minimizeif not completely eliminate fouling deposit formation. In this regard,we have discovered that a considerable reduction in deposit formationrate can be effected by adding a fouling inhibiting amount ofmechanically degraded polyisobutylene to the hydrocarbon stream incontact with process equipment at elevated temperatures. f

It is therefore one object of this invention to provide a method forreducing the formation of fouling deposits in hydrocarbon processsystems. Yet another object of this invention is to prevent or at leastminimize the formation of fouling deposits in the interior ofhydrocarbon processing equipment. Yet another object of this inventionis the reduction of fouling deposit formation on heat exchange surfacesin contact with hydrocarbon media. 7

In accordance with one embodiment of this invention the fouling depositformation rate in hydrocarbon processing equipment in contact withfoulant producing hydrocarbon oils at elevated temperatures, e.g., aboveabout 250 F is reduced by the addition of a foulant inhibiting amount ofmechanically degraded polyisobutylene.

The foulant inhibiting compositions of this invention can be employed incombination with essentially any hydrocarbon process stream includinglight distillates, e.g., naphthas, kerosenes and the like, middledistillate stocks from cracking operations, virgin crude oils, toppedcrude oils, etc. The great majority of hydrocarbon streams usuallyemployed in such processes boiled above about 200 F. However, thegreater fouling problems are usually associated with high boilingstocks, particularly in those containing a substantial portion ofunsaturated hydrocarbon constituents boiling between about 400 and 1,200F. Hydrocarbons boiling substantially above 1,200 F. generally decomposeon heating to temperatures above that point. Therefore, most feeds aregenerally characterized as having top and boiling points of 1,200 F. orless. Hydrocarbon mixtures which generally exhibit the greatestpropensity for producing foulant deposits are those containingunsaturated hydrocarbons, e.g., olefins and aromatics usually in amountsof at least about 5 volume-percent and generally in excess ofvolume-percent. Olefin concentrations are usually in excess of about 5volume-percent.

The fouling problem associated with these hydrocarbon mixtures isgenerally promoted at elevated temperatures. The mechanisms are believedto involve polymerization or a combination of polymerization andoxidation which in some respects are similar to the mechanisms leadingto gum formation in gasolines. The high temperatures attained in heattransfer or other process steps are believed to promote the combinationof hydrocarbons with oxygen to form a polymeric material that maydeposit on the surfaces of process equipment, particularly in heattransfer areas.

Although fouling promoted by this mechanism, i.e., oxidativepolymerization and the like, might be controlled by excluding oxygenfrom the process, that objective cannot always be economically achieved.For example, the ordinary floating roof tanks in which feedstocks arefrequently stored are not completely effective in preventing contact ofthe hydrocarbon with atmospheric oxygen. Furthermore, many feedstockscon tain oxygen as they are received at a refinery or at a process site.Consequently the utilization of other alternatives for the prevention offoulant formation such as the antifoulant compositions of this inventionare often necessary.

It is presently believed that these antifoulant compositions operate inone of two ways or a combination of both to effect reduction of foulantdeposits. They may either prevent the formation of high molecular weightpolymeric material or highly condensed polynuclear aromatic carbonaceousdeposits in hydrocarbon process streams by interferring with thechemical mechanisms necessary to the formation of such agents. On theother hand, a mechanically degraded polyisobutylene herein described mayreduce the affinity of the process equipment surfaces for the polymericor carbonaceous substances once formed, thereby maintaining thosematerials in solution in the form of small dispersed particles orglobules exhibiting relatively low fouling tendencies. This finding israther surprising particularly in view of the marked superiorityexhibited by mechanically degraded polyisobutylenes as compared tonondegraded isobutylene polymers lending a unique utility to thesematerials that provide a number of substantial economic advantages. Theconclusions are believed reasonable in view of the substantial savingsto be realized by either preventing or reducing the frequency of unitshutdown and turnaround necessitated by excessive heat transfer or fluidflow loss due to fouling. The expense involved in such unit shutdownsdue to both maintenance expenditures and loss in operating time isgenerally well known and need not be elaborated upon herein.

Due to the nature of the mechanism believed to account for the observeddeposit formation, the problem is usually noticed at temperatures aboveabout 250 F. and generally within the range of about 350 to about 800 F.Temperatures substantially above this upper limit of 800 F. usuallyresult in some thermal cracking which is generally undesirable.

Numerous procedures available for producing isobutylene polymerssuitable for application within the concept of this invention aregenerally well known and need not be described in detail herein. Themechanically degraded polyisobutylenes presently preferred in thisinvention are prepared from polymers having a viscosity-averagemolecular weight within the range of about 100,000 to about 400,000. Thedesired degree of mechanical degradation is conveniently effected bysubjecting the polymer either in the molten state or in the form of arelatively concentrated solution, i.e., between about 5 andweight-percent polymer in a compatible solvent such as aliphatic and/oraromatic hydrocarbons having up to 30 carbon atoms per molecule, tomechanical shear of severity sufficient to break down the polymerlinkages. Shear rates on the order of at least about 1,000 reciprocalseconds and preferably 5,000 to about 50,000 reciprocal seconds arepresently preferred. Contact times at the shear rates necessary toeffect the desired degree of mechanical degradation are usually at leastabout 5 minutes, preferably 5 to about 30 minutes.

A particularly effective indicator of the degree of degradation achievedis the Brookfield viscosity of a relatively dilute solution of degradedpolymer as compared to a similar solution of nondegradedpolyisobutylene. As a general rule, it is preferable to reduce theBrookfield viscosity of a 5 weightpercent solution of the originalpolyisobutylene in a standard solvent, e.g., kerosene, by a factor of atleast about 10, preferably 20 to about 500. The resulting degradedpolymers generally have Brookfield viscosities within the range of aboutto about 10,000 centipoise.

The exact nature of the modification affected by mechanical degradationwhich accounts for the marked improvement in fouling inhibitionexhibited by the degraded polymers is not known with certainty. Aspreviously mentioned, the observed results may be attributable either tochemical or physical modifications of the polymer or a combination ofboth.

Even minute amounts of the degraded polyisobutylenes are effective forreducing fouling rates. However, any substantial degree of improvementgenerally necessitates the use of at least about 0.5 ppm of the degradedpolymer. Concentration levels within a range of 1 to about 100 ppm aremost common although it is presently preferred to employ about 1 toabout 50 ppm of the polymer in most systems. The lower concentrations,i.e., up to about 50 ppm are presently preferred in view of observationsbased on experimentation to date indicating that concentrations of 50ppm and above do not appear to provide the same degree of advantagerealized with somewhat lower amounts of polymer. This observation itselfis rather anomalous and is as yet unexplained. Nevertheless, in view ofthese observations there is little to be gained by employing polymerconcentrations substantially in excess of 100 ppm in view of the addedexpense associated with high polymer concentrations, which are notpresently justifiable on the basis of improved performance.

The following examples are presented to illustrate the effectiveness ofthe described procedures and should not be con strued as limitingthereof.

EXAMPLES l-l2 These examples were run-sequentially with differentfouling inhibitors and inhibitor concentrations in a two-stage preheateremploying a feed boiling between 307 and 701 F. containing 30volume-percent aromatics, 1 percent olefins and 69 percent saturates,and having an API Gravity of 33.5 at 60 F.

The two preheaters were operated in series with the first heateroperating across a temperature range of 75 F. to 425 F. and an outlettemperature of 600 F. Each heater constituted an elongate tubular shelland an axially disposed resistive heater defining an annular crosssection for the passage of the process stream. This apparatus was amodification of the Erdco coker originally developed to test the thermalstability of turbine fuels in accordance with ASTM Dl 660. The ASTMapparatus usually employs aluminum tubes and filters upstream anddownstream of the apparatus. In order to obtain more adequatediscrimination between these several fouling inhibitors in thisinvention, the ASTM Erdco Coker apparatus was modified by removal of thefiltering systems and substitution of a carbon steel tube for theoriginal interior aluminum tube surrounding the resistive heater. Thesubstitute carbon steel tube was of the same dimensions as the originalaluminum apparatus and could be removed for weighing to determine theamount of weight gained during a specified period of operation. Asalready mentioned, further modification included the use of two of theseErdco Coker tubes in series to more closely simulate the operation ofseries stage heat exchange at different temperature levels.

During each run the antifoulants were injected into the hydrocarbonstream upstream of the first heating stage and the hydrocarbon-additiveadmixture was continuously passed through the series heaters at a rateof 4.5 pounds/per hour corresponding to -a linear flow rate of 0.07 feetper second through each heater. Each run was continued for 90 minutes atthe .conditions and with the compositions illustrated in the table. Theheat exchange tubes were weighed before and after each period ofoperation to determine the weight gain attributable to fouling depositformation.

The mechanically degraded polyisobutylene in Examples 8 and 9 wasprepared by shearing a kerosene solution of weight-percent Oppanol B-200having a weight-average molecular weight of 200,000 in a Waring Blenderat a shear rate of approximately 20,000 reciprocal seconds for a periodof to about minutes sufficient to reduce the Brookfield viscosity of thesolution from its original value of 37,800 centipose at 6 rpm to a finalvalue of 365 centipose at 6 rpm. The resultant kerosene solution of thedegraded material was then added as such to Examples 8 and 9 in theproportions indicated. I

TABLE Amount Wt. Gain of Tubes, gms Exp. Additive ppm 1st Tube, 2ndTube,

1 None .0059 .0616 2 None a .0083 .0622 3 UOP Polyflo 135 10 .0063 .03584 Oppanol 13-200 50 .0178 .0370 5 Betz Al -104 10 .0120 .0719 6 OppanolB200 10 .0080 .0147 7 None .0098 .0362 8 Oppanol B200 10 .0059 .0010Degraded 9 Oppanol 5-200 50 .0051 .0394

Degraded l0 Nalco 261 10 .0042 .0117 1 1 UOP Polyflo 140 10 .0077 .018512 Tretollte Aftol The results of these examples illustrate that themechanically degraded polyisobutylene (degraded Oppanol B-200) evidencedantifouling characteristics markedly superior to those of the otheravailable fouling inhibitors, particularly at lower concentrations,i.e., 10 ppm. The undegraded polyisobutylene actually increased thefouling rate in the first tube having an outlet temperature of 425 F. asillustrated by the weight gain in Example 4 of 0.0178 grams at a levelof 50 ppm of additive. However, the undegraded polyisobutylene of thatexample was effective in reducing the weight gain in the second tubefrom about 0.06 to about 0.037. This performance was markedly improvedat the lower concentrations of undegraded polyisobutylene as illustratedin Example 6. In that example employing 10 ppm of the undegradedpolyisobutylene the fouling rate in the first tube was only 0.008 gramsfor a 90 minute operation while the weight gain for the same period inthe second tube was reduced to 0.0147 grams. The improvementsattributable to mechanical degradation of polyisobutylene are apparentfrom comparison of these examples, i.e., Examples 4 and 6 to Examples 8and 9. In Example 9 the 50 ppm of mechanically degraded polyisobutylenewas sufficient to'reduce fouling in the first tube to 0.0051 gmsaccounting for a substantial reduction as compared to the weight gain of0.0178 gms observed with 50 ppm undegraded polyisobutylene in Example 4.The weight gain in the second tube of both of these examples wasapproximately the same. However, at 10 ppm the mechanically degradedpolyisobutylene employed in Example 8 was effective not only in reducingthe weight gain in the first tube to 0.0059 gms but dramatically reducedfouling in the second tube to a level of only 0.001 gms, 11 times lessthan the next lowest value observed in Example 10 with Nalco 261. Theadvantages of this procedure are readily apparent from theseobservations.

WE CLAIM:

l. A method for reducing the fouling rate in process equipmentcontaining foulant producing hydrocarbons boiling above about 200 F. attemperatures above about 250 F. which comprises admixing with saidhydrocarbon oil at least about 0.5 ppm of mechanically degradedpolyisobutylene having a Brookfield viscosity within the range of aboutto about 10,000 cp.

2. The method of claim 1 wherein said hydrocarbon contains at leastabout 5 volume percent of unsaturated constituents including olefins andaromatics and is admixed with an amount of said mechanically degradedpolyisobutylene within a range of about 1 to about 100 ppm.

3. The method'of claim 1 wherein said hydrocarbon contains at leastabout 15 volume percent of unsaturated hydrocarbon constituents selectedfrom olefinic and aromatic hydrocarbons, said hydrocarbon boils within arange of about 400 to about 1,200 F. and is contacted in said processequipment at a temperature within the range of about 350 to about 800F., and said mechanically degraded polyisobutylene is produced bysubjecting a polyisobutylene polymer having a viscosity-averagemolecularweight within a range of about 100,000 to about 400,000 to a shear rateof at least about 1 ,000 reciprocal seconds for at least about 5minutes.

4. The method of claim 1 wherein said hydrocarbon boils within the rangeof about 400 to about 1,200 F. and contains at least about 15 volumepercent of unsaturated hydrocarbon constituents selected from olefinicand aromatic hydrocarbons, and said hydrocarbon is contacted in saidprocess equipment at a temperature within a range of about 350 to about800 F. in the presence of about 1 to about 50 ppm of said mechanicallydegraded polyisobutylene produced by subjecting an isobutylene polymerhaving a weight-average molecular weight within a range of about 100,000to about 400,000 to mechanical shear sufficient to reduce the Brookfieldviscosity of a 5 weight-percent solution of said polymer in kerosene bya factor of at least about 10.

5. The method of reducing fouling rate in hydrocarbon heat exchangeequipment operating on hydrocarbons boiling within a range of about 400to about l,200 F. and containing at least about 15 volume-percent ofunsaturated hydrocarbons selected from olefinic and aromatichydrocarbons at a temperature within a range of about 350 to about 800F. which comprises contacting said hydrocarbons in said heat exchangeequipment in the presence of at least about 0.5 ppm of mechanicallydegraded polyisobutylene having a Brookfield viscosity within the rangeof about 100 to about 10,000 cp.

6. The method of claim 5 wherein said mechanically degradedpolyisobutylene is prepared by subjecting polyisobutylene having aviscosity-average molecular weight within a range of about 100,000 toabout 400,000 to a shear rate of at least about 1,000 reciprocal secondsfor at least about 5 minutes.

7. The method of claim 5 wherein said mechanically degradedpolyisobutylene comprises about 1 to about 50 ppm of said hydrocarbonphase and is prepared by subjecting said polyisobutylene having aweight-average molecular weight within the range of about 100,000 toabout 400,000 to a shear rate and for aperiod of time sufficient toreduce the Brookfield viscosity of a 5 weight-percent solution of saidpolymer in kerosene by a factor of at least about 10.

8. The method of claim 5 wherein said foulant producing hydrocarbon feedis selected from normally liquid light distillate, middle distillate andresidual hydrocarbon fractions and combinations thereof, and saidmechanically degraded 400,000 to mechanical shear at a rate and for aperiod of time sufficient to reduce the Brookfield viscosity of a 5weight-per- 7 cent solution of said polymer in kerosene by a factor ofat least about 10.

k i l

2. The method of claim 1 wherein said hydrocarbon contains at leastabout 5 volume percent of unsaturated constituents including olefins andaromatics and is admixed with an amount of said mechanically degradedpolyisobutylene within a range of about 1 to about 100 ppm.
 3. Themethod of claim 1 wherein said hydrocarbon contains at least about 15volume percent of unsaturated hydrocarbon constituents selected fromolefinic and aromatic hydrocarbons, said hydrocarbon boils within arange of about 400* to about 1, 200* F. and is contacted in said processequipment at a temperature within the range of about 350* to about 800*F., and said mechanically degraded polyisobutylene is produced bysubjecting a polyisobutylene polymer having a viscosity-averagemolecular weight within a range of about 100,000 to about 400,000 to ashear rate of at least about 1,000 reciprocal seconds for at least about5 minutes.
 4. The method of claim 1 wherein said hydrocarbon boilswithin the range of about 400* to about 1,200* F. and contains at leastabout 15 volume percent of unsaturated hydrocarbon constituents selectedfrom olefinic and aromatic hydrocarbons, and said hydrocarbon iscontacted in said process equipment at a temperature within a range ofabout 350* to about 800* F. in the presence of about 1 to about 50 ppmof said mechanically degraded polyisobutylene produced by subjecting anisobutylene polymer having a weight-average molecular weight within arange of about 100,000 to about 400,000 to mechanical shear sufficientto reduce the Brookfield viscosity of a 5 weight-percent solution ofsaid polymer in kerosene by a factor of at least about
 10. 5. The methodof reducing fouling rate in hydrocarbon heat exchange equipmentoperating on hydrocarbons boiling within a range of about 400* to about1,200* F. and containing at least about 15 volume-percent of unsaturatedhydrocarbons selected from olefinic and aromatic hydrocarbons at atemperature within a range of about 350* to about 800* F. whichcomprises contacting said hydrocarbons in said heat exchange equipmentin the presence of at least about 0.5 ppm of mechanically degradedpolyisobutylene having a Brookfield viscosity within the range of about100 to about 10,000 cp.
 6. The method of claim 5 wherein saidmechanically degraded polyisobutylene is prepared by subjectingpolyisobutylene having a viscosity-average molecular weight within arange of about 100, 000 to about 400,000 to a shear rate of at leastabout 1,000 reciprocal seconds for at least about 5 minutes.
 7. Themethod of claim 5 wherein said mechanically degraded polyisobutylenecomprises about 1 to about 50 ppm of said hydrocarbon phase and isprepared by subjecting said polyisobutylene having a weight-averagemolecular weight within the range of about 100,000 to about 400,000 to ashear rate and for a period of time sufficient to reduce the Brookfieldviscosity of a 5 weight-percent solution of said polymer in kerosene bya factor of at least about
 10. 8. The method of claim 5 wherein saidfoulant producing hydrocarbon feed is selected from normally liquidlight distillate, middle distillate and residual hydrocarbon fractionsand combinaTions thereof, and said mechanically degraded polyisobutylenepolymer is present in an amount within the range of 1 to about 100 ppmand has a Brookfield viscosity within the range of about 100 to about10,000 and is prepared by subjecting polyisobutylene having aviscosity-average molecular weight within a range of about 100,000 toabout 400,000 to mechanical shear at a rate and for a period of timesufficient to reduce the Brookfield viscosity of a 5 weight-percentsolution of said polymer in kerosene by a factor of at least about 10.